How to look up older recorded sales?

For co-op sales from 2003, and condo sales back to the 1960s, see http://www.nyc.gov/html/dof/html/jump/acris.shtml

The 2003 and 2004 links here (http://www.nyc.gov/html/dof/html/property/property_val_annual_sales.shtml) provide limited but more user-friendly (vs. ACRIS itself) ACRIS sales data for the period immediately prior to the beginning of SE's co-op price histories. Also, SE now goes back to 1990-something (1995?) on condos. Co-ops are since 2004.

This is great, thank you both. Was trying to look up sales in a particular coop building earlier than 2004, so it seems like this info doesn't exist earlier than 2003, then?

The managing agent for the building might have this information for the building, as they are usually the conduit for sales in the building - but probably will not give it out.